Radio paging for vehicles



` March 2, 1948. R, K POTTER RADIO PAGING FOR- VEHICLES Filed Dec. 22,1944 3 Sheets-Sheet -1 .wv N/W 1 nl, m. l |11 .E A

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' March 2, 1948. R, K POTTER RADIO ,PAGING FOR VEHICLES 3 Sheets-Sheet 2Filed Dec.

EN Si Qml /NVE/vrof? RK. POTTER ATTORNEY March 2, 1948. R. K. POTTERRADIO PAGING FOR VEHICLES 5' Sheets-Sheet 5 Filed Dec. 22, 1944 an m m NMPM wK/Z. EN .R v v1 mN present invention operates as follows.

Patented Mar. 2, 1948 2,436,824 v l mimo PAGING Foa VEHICLES Ralph K.Potter,

Bell Telephone Laboratories,

Morristown, N. J., assignor to Incorporated.

New York, N. Y., a corporation of New York Application-December 22,1944, Serial No. 569,347 12 Claims. (Cl. Z50-6) This invention relatesin general to communication systems and in particularto radio systems inwhich a single radio transmitting station can selectively signal any oneof a plurality of subscribing units. v

The need has been-recognized for a Simple and inexpensive method ofcommunication to enable drivers of vehicles en route from one point toanother to be apprisedk of awaiting messages. Such a service isespecially adapted for :use by buses and trucks traveling overextendedroutes and by professional persons Such as doctors or salesmenobliged to make a series of consecutive calls in their private'vehicles.-Howeven the system herein disclosed conceivably has many other uses.While radio calling or annunciator Systems of the type disclosed in anarticle entitled Radio telephone signallingfby Charles S. Demarest,Milton L. Almquist, and Lewis M. Clement, Journal of the AmericanInstitute of Electrical Engineers, volume 43, March 1924, have beenemployed in ship to ship and ship to shore communication, and Similarsystems have been utilized for train dispatching and air-transportcommunication, the apparatus used for these purposes is in generalsomewhat expensive and cumbersome for the typeof service primarilyenvisioned by the applicant.

`It is therefore theprincipal object of this invention to provide yasimple means for radio paging of vehicles whereby conventional broadcastprogram receiving equipment is utilized at least in part for callreception by subscribing units. Y

Another object of this invention is to provide an inexpensive meanswhereby one of a plurality of subscribing stations may be selectivelysignalled by the calling transmitter.

A. still further object of this invention isto prow/idea method forincreasing the number of subscribing units which can be served withfacility by a single call transmitting" unit without appreciablyincreasing the cost and size of the transmitting equipment. Y

Additional objects will be apparent upon consideration of the followingspecification.

In a preferred embodiment, the system ofthe A message for a, callingservice subscriber is communicated to an operator at thetransmitterstation. The operator then selectively signals the designated vehiclesubscriberstation whereupon some signal device, such as a lampor a bell,referred to variously hereinafter as, an announcing device or signalannunciator operates to notify Y the subscriber that a message awaitshim. vThereupon he may communicate with the calling transmitter stationby telephone jat his'earliest convenience to learn the message.

. Certain phrases and terms as 4used hereinafter 1 y in thespecification and claims will be defined as follows. y

The phrase calling carrier frequency refers to oscillations preferablybut not necessarily of an order of frequencies which is the same as orhigher than that of the conventional broadcast range; while the phrasemodulating frequencies refers to frequencies of the order of 15kilocycles or less.V

Message translator refers to any device such as a loud Speaker or an inkrecorder connected tothe audio stage of a conventional high frequencyreceiver whereby the audio modulations of carrier frequency theredetected and amplified are translated rinto such a form as to conveymeaning to a receiving operator. l VMobile unit refers to any body whichmay be moved with facility from one place to another. .The phaseselector unit or selector mechanism refers to mechanisms of a type Wellknown in the art whereby one of a plurality of local units may besignalled in preference to the others byvirtue of the fact that thelocal circuits contain uniquely placed contacts each of which is engagedat a dierent instant during a Stated time interval by contactors or armsmoving synchronously in all of the localunits. The selector arm usuallybut not necessarily moves in rotary fashion about an axis, an attachedbrush engagingcontacts fixed at desired points on a dial.

:The calling apparatus in a, preferred embodiment comprises a source ofradio-frequency carrier oscillations which are fed from a transmitteronto an antenna as a Series of pulses, the duration and timedrelationship of Which are controlled by a clock-driven selectormechanism. Removable contact plugs connected to the pulsing means of thetransmitter may be inserted into jacks on'the selector dial .s'o thatone or many desiredsubscribing stations can besignalled during aparticular selector cycle which may be defined as that time intervalduring which trie selector arm moves from the home position through allthe positions on the Selector dial and returns again to the homeposition. Ina preferred embodiment, the call receiving apparatus maycomprisethe conventional broadcast receiving` antenna coupled to areceiver of the type ordinarily employed in automobiles Awhich can betuned eitherto the broadcast range or to a calling frequency carrierwave. The conventional dash-board clock mechanism furnishes the motivepower for operation of the selector which is connected to one optionalcontact of a two-way switch the common pole of which is connectedto theaudio output Y of a conventional receiver and the other optional contactof which is connectedv to a conventional broadcast loudspeaker,V broadlydesignated in the claims hereinafter'as 'a message indicator or messagethe clock-driven selector mechanism preparatory to receiving signalsfrom the calling system. A

plug electrically connected to an an n uriciatorV device is fixed at apredetermined position on the subscribers selector dial, 'Aft'er thetsub-` scriber tunes his broadcast receiver tothe calling carrierfrequency and operates 'the switch cutting ofi the loud-speaker or othermessage indicator, the rst received pulse of calling carrier frequencyinitiates operation of the selector mechanism. When that particularsubscribers station is called, a second carrier frequency pulseV isreceived at that instant when the selector arm at'that 4station engagesthe contact plug, causing a signal device to operate indicating a call.

It is therefore 'significantthataccording to this invention onlythe'functionswitch, theselector, and the clutch with itsclutch'mechanismneed be added to the conventional car `dasli-board radioand clock equipment to enable vany'particular vehicle'to'b'ecome aparticipating member of the calling system.

Inv one embodimentof the invention, acentral transmitting unit ofcarrierifrequency isprovided with apparatus for simultaneously'sendingout signals of several diiferent audio modulations. To each'audio'circuia aseparate select-or'unit vis connected, Vso that `such atransmitting station is thus' enabled toserve several times as "manysubscribers Vas can conveniently'be' accommodated'in a selectivesignalling or annunciator system utilizing pulses of carrier frequencyWithout audio frequency modulation A tuned-circuit placed vin eachsubscribers selectorcircuit causesthat particularcircuit when connectedto itsirespectivejbroadcast receiverto be responsive to only' one oftheaudio frequenci'e sent out by the calling transmitter.

The 'invention will be 'better understo'od'from' a study of the detaileddescription of 'several embodiments of the features'thereof as'givenhereinafter and'by reference'to the accompanying drawings, in'which:

Fig. `1 'is a schematic diagram of apreferre'd embodimentA of a callingsystem for vehicles shwing` a typical call transmitter 'and callreceiving unit;

Fig. '2Ashows schematically alternative selective signalV receivingmeans which mightibe in'- corporated in a`v calling'system in'accordance with the invention; Y

Fig. 2B is a side elevation of the clock-driven selector mechanism ofFig. vZ'Ashowing in detail lead Wires 2 from the oscillator and the leadwire 2a to the transmitter in response to energization oftheelectromagnet 5. "En'erg'ization' yof the electromagnet"5whichiselectrically connected to the .battery 6 and the ground connection 'I iscontrolled by the clock-driven selector mechanism 8.

Theselectgr;mechanism 8 operates as follows.

'seY

When the transmitting operator presses the key 9'-causin'gthelgroundfconnection I0 to be engaged, 1b

electromagnetl 'and the battery I2 to ground "connection r I3. Thusenergized, the electromagafcircuit'isicllpleted through the windings ofthe net I rIA actuates its movable solenoid core constituting part ofthe clutch I5 thus mechanically :coupling clock shaft I4 to the selectorarm I6. Rotation 'of the *cl'ck shaft |14 rby the clock mechanism I lwhichfis" l`ele ctr'ially connected to theI battery I9 and thegroundEconnection 2i), causes the selector armto "movev around the selectordial. When the brush I 6a on 'the selector arm I6 engagesthejc'onducting ring 22, the circuit Vof the electromaghet I l isconnected through the resistor 24,`ring `22, brushl Ia and selector armI6 tothe -groundconnection 23, thus causing lectro'rnagnetl IIto remainenergized after release ofthev key S'by'th'e operator. This locks theselector arm I6 in engagement with the clock shaft I4 for the `durationofthe cycle, i. e., until brushv Ia, disengages ring 22, so'that saidselector arm continues to m've around the selector dial. The first lstepthrough which selector army I6 moves after motion `thereof has 'beeninitiated brings it into' engagement with contact 25 which ispermanently connectedthrough the lead Z to the winding of 'electromagnet5. Connection through thevselector arm I6 tothe ground contact 23 causesthe' electromagnet to be momentarily energized thus'actuating thearmature 4to close the circuit 2-2a'whereby a pulse of carrier frequencyoscillations is transmitted. As the selector arm 'I6 moves 'o'n' aroundthe dial, it males electrical contact with-'whichever of the plugs 21are Dlaced in the J`acl s'.?8,r each of which represents a differentsubscribing station inthe selector lcyc'le. IVS/'hen'ftle selector armIS contacts a givenplugfZ'Ijwhich has been previously placed inthecorresponding'jack 2 8, the circuit is closed from the ground' contact-23 through the brush I-Sa. and plug 21 connecting wire 29, the windingsof thef l'exgtromaety 5, and the battery 6 -'to ground'l. AsLatthe'initial step, the electromagnet 5-'is"again 'energized wherebythe armature'4 is actuated to closethe 'circuit' 2- -2c tr thus )causingpulses of carrier frequencyoscillations to Vbe transmitted fat desiredinstants in the selector cycle, corresponding :to particular subscribingstations to be called.

mechanical means for "coupling 'the selector mechanism to'the'driving'shaft ofthe clock; and

Fig. 3 is a schematic 'diagram of a modified calling system in which thecalling carrier frequency is modulated according toseveral'distinctaudio frequencies. Y

A typical vehicle calling system according to the inventi-on may, asAshown'in Fig. 1 of the drawings, embody the follo'wingfeatures. Carrierfrequency oscillations are supplied from the radio frequency oscillatorI,'which may be of any well-known type, through 1a circuit 2-'2a to theradio transmitter 3 from which the oscillations `are fed ontothe'transmittingantenna' 3a.

The transmittedcarrier' vfrequency oscillations are pulsed by means of"an armaturellwhich I'I'l'aksand breaks 'contactwbetween" one of the`One embodiment 'of a'` call receivingf'apparatus for subscribers asshown schematically inFig. 1 opeates'asfollws. 'A pulse'ofcarrierfrequency received bythe I'anter'ina v"30 passesto ground throughthepr'imary 3| of the transformer 33 thereby inducing anelectromotive'force inthe transformer second-aryy 32. 4The tuning means 34, which maycompriseeither a single variable' con- `denser or ablock of condensersin series and/ or parallelarrangernent, may be varied over a range thatincludes the callingca'rrier frequency in addition to the conventional;broadcastrange of frequencies. The incorning signal to'which the4circuit 32-i34 is tunedM passes' into the receiver"35, whichjrnaybe ofrany "well-known type, but is preferably"a typeS/'liitable for 'use inaconventionalZdashY-board car'radio .,unfit. .'Iheidirect currentoutput'froni'the adiode'tector lo1 thereceiver 35 83 to the loud-speakeror' other message translating unit 42. This is the condition forordinary broadcast reception.

In order to condition the apparatus to receive calls from the callingtransmitter, the tuning means 34 is tuned vto the calling carrierfrequency of transmitter 3 and the switch 31 is positioned to closecontacts 38 and 39 thereby' cutting off the loud-speaker 42, andconnecting the audio detector of the receiver 35 to theclockdrivenselector mechanism 48. Received calling carrier signals thenpass from the antenna 30 through the transformer' 33, the tuned circuit32-34 to the receiver 35, and the resulting space current from thedetecting circuit passes by Way' oflthe -switch31and the Winding of theelectromagnet 43 to ground 44. "An alternate path to ground 44al throughthe condenser-44h is provided to shuntalternating current remaining inthe output of the-receiver 35 away from the windings ofI the magnet 43.The electromagnet 4'3 should be understood to'be of a -marginal typeresponsive to direct current such that any minute current which mayrowin the absence of calling signals Awill be insuicient to energize therelay,4

but the increased current occurring upon detection will exceed themargin and operate the relay. vThus energized, the electromagent 43actuates the armatures 45 and 41, thereby connecting the ground 45throughthe connecting Wire 49, to the circuit ofthe electromagnet 50,which is connected to the battery 5l and ground 52. The

electromagnet 50--is then caused to -actuate its movable solenoid corewhich constitutes part of the clutch 53 thereby mechanically couplingthe clock shaft 54 to the selector arm 58. l As in the transmitterapparatus described hereinbefore, rotation ofthe clock shaft 54 which iselectrically connected through the battery 51 to ground 59, causes theselector arm 58 to move around the selector dial. As soon as the brush58a on the selector arm 58 contacts the ring 60, the ground.'

6| is applied through the resistor 62 'to the circuit ofthe'electromagnet 5D, thereby causing the electromagnet 50 to remainenergized after the cessation of the initial calling pulse whichenergizes the electromagent 43, and thus locking the clutch 53' inoperation for the duration of the selector cycle, i. e., until brush 58rdisengagesi ring 68. The selectork arm 58 moves around the selectordial untilV it engages the annunciator contact plug 82 which is iixed inan appropriately positioned jack 8l. Each subscribing station has aunique position on the dial. In the particular subscribers unit beingcalled the second pulse of calling carrier `frequency received throughthe antenna-*30, passes through the transformer 33, the tuned circuit32-34 and into the receiver 35. The direct current output,

which is then taken from the audio detector of the receiver 35, passesthrough contacts 38 and 39 of switch 31, and the windings of theelectromagnet 43 to ground 44, thus causing the electromagnet 43 to beenergized at the instant when the arm 58 is in engagement with the plugvcontact 82. The armature 45 ls actuated completingv thelclin'g circuitofthe electromagnet 5|);l 'andv the armature 41 rlsactuated completing acircuit from 'the'ground Gl'through the selector arm 58,' the contact82,the-windings of theelectromagnet the loud-speaker 42 through the audioamplier s4; andv the battery 65 tigrounu s6. Energiza-l tion of 'theelectromagnet 64' actuates the arma.- ture 61 to close circuit'from theground 18 through lthe signal lamp 69, armature 61, and

.thebattery 65 to ground 66, thus causing the signal lamp-69 to light.Simultaneously, the armature 68 is actuated to'apply the ground contact10through the normally closed contacts of key' -1I and armature 68 tothe circuit of the Yelectromagnet 64, causing it 'to vremain energizedafter the cessation of the pulse, and thereby locking the signal lamp 69in operation. Depressing the'key 1| will disconnect the ground v10 fromthe circuit of the electromagnet 64, thereby deenergizing it-and causingthe signal lamp 69 to bey extinguished,

It will be apparent that each of the various receiving stations whichare to be called will have its annunciator energizing selector contact82 at a position individual to and characteristic of that Consequently,a.

-provided as will "aiford the necessary selective factor Which'is, ofcourse, dependent yupon the diiference in lthe time interval occasionedby passing from a selector contact position tothe nearest adjacent one.A particular advantage vof the system l.is that additional mobilestationsV may be' added by the vuse of apparatus identical with thatused at the other mobile stations eX- cept for the position of thecontact 8| to which the lead .to the annunciator circuit is connected.

` A modified embodiment of a receiving unit, according to the invention,is shown in Fig. 2A of the drawings. Y Members identical in structureand function lwith corresponding members of the system of Fig. '1' willbe designated by correspondingl reference characters. As in Fig. 1, thecarrier frequency' signal is received by the antenna 38, vfrom which itpasses through `the transformer 33 andtuning means 34 to the radiofrequency stage'of the receiver 35. The amplied,

detector signal is conducted from the audio.

detector ofthe receiver 35 to the common terminal 38 of the double-throwswitch 31. As in Fig. ljwhen the apparatus is utilized for ordinarybroadcastreception, the switch 31 is positioned to connect points 38 and40, thereby coupling 83 and the transformer 4I to the audio detector ofthe receiver 35.

' When the tuning means 34 is tuned tothe calling carrier frequency andthe switch 31 is positioned to engage contacts 38-39 thus cutting olfthe amplifier 83 and the loud-speaker 42 and electrically coupling theVclock-driven selector mechanism 48 to the-receiver 35, -the apparatus isin condition to receive calling signals as follows. An initial pulse ofcalling carrier frequency is received by the antenna 30 and passedthrough the transformer 33 and the tuned circuit 32-34 to the receiver35'where it is amplified and detected. Current from the audio detectorof the receiver 35then passes through contacts 38 and 39 of the switch31, through the windings of the electromagnet 43 `to ground 44. Theelectromagnet 43' ris of a marginal type as described with reference tothe apparatusorFig. 1. Y e

'j' The mechanicalarrangement utilized for coupling the selectormechanism to the drive shaft in Fig. Z'is aftype'offriction clutch wellknown 'onerof the jacks 8l annunci.

in the art. ts operation "Will-beV better underflstood by .reference toFig. 2B of thedrawings.y

When the selector mechanism 48' is notin opa eration, the clock shaft 54driven bythe; clock mechanism 55 rotates carrying with-it the collars 18and 11a, and the spring.; '|65` attachedthere-k between. The spring 16acts through al splinerto maintain a sliding frictionalcontact betweenthe` matching surfaces ofthe rotating collar 11a andA the collar 11bWhicliv remains -xedas longv as the. arm 14 isl held `in positionpby thelatch-ing ar;-

plete rotation with the 'shaft 54, carrying with` it the stop arm 14 andthecontactarm58. When the arm 14' returns to its start-ing point itl isagain latched in position by thearmaturev 1 3.

The removable contact plug. 82- is. inserted in calling service. As thecontact arm`58fmoves around the selector dial, it. en'gagesthefcontactplug 82 during the course,oftherotation-. VIn.

the particular subscribingV unit which. is being called, a second pulseof calling.l carrier frequency is received bythe antenna SIIVampliiiedand detected by the receiver at the-instant when the contact arm 58engages theI contact plug 82; The detector output from the;receiver-35vthen in a position 'assignedY uniquely to each particularlsubscriber by the passes through the'l contacts V38 and 39 of' the`switch 31 and by way of `the lead 96fthrough the` relay 43 to ground 44;Current'also `passesover a parallel path by way. of the conducting Wire95 through the brush 86 whichA rides onthe shaft 54', wherebyelectricalcontact established with the contact arm 58'closing.theicixcuit through the plug 82; The relay 64' Whichis: of themarginal type,yis1 energized, actuating the relay armature 68', therebyclosingthe circuit from the power source 51?, andcausingthe lamp 69' tobe lighted and locked in operation. The lamp ,69' may be extinguishedgbydepressing the key 1I thereby breaking the circuit to the bat-Y tery51..

As stated in the description ofFig, 1 above,

the number of receiving stations which may bek selectively called by asingle transmitter depends on the number of individual.contact`positions which may be 'accommodated with thevrequired degree ofselectivity in a single selector cycle.

vInorder to make `it possible -for a-'sin'gle trans-` mitter toaccommodate a lar-ger number oi'sub-` scribers than wouldI be possible`Kby use ofthe systems described withreferenceto Figs. l4 an ld.2` of thedrawing, another embo'di'mentof the in;

vention employs audio `frequency modulation "l" the tined carrierfrequency `pulse'sw s'nt' out by. the calling service' transmitter; t Y

The system Vof Fig; s which i'scresigneditb `sndrtaneously transmit 'anumber "of V"ep'arate signals. each having thesamecarrier Threedifferent audio frequency' signals `from a modulating circuit of:s'ometype well'knowniinn l l equn'cy but a different audio modulation',operatesas follows.:

the art with a carrier frequency oscillator andy conventionaltransmitter such asare indicated separately as elements. lIV and 3v ofFig. 1; The functionA of the band-pass filters 88A, 88B and 88C is' toprevent the transientsproduced by the operation of the relays. frombeing transmitted and possibly ycausing false operation. Before beingfed into the transmitting unit 9|, the three different audio 4signalsare pulsed by means of `armatures 4A; 4B and 4C which are responsive toelectromagnets 5A, 5B and 5G, respectively. The energiza-tion ofelectromagnets 5A, 5B and 5C vis controlled` in each case by means of acorresponding separate selector unit 8A; 8B or 8C,

. each of which operates :in the .manner described hence, the number of.separate systems to be usedv in anyV particular calling system, need notbe limited to three as shown in the foregoing example, but may be anynumber which can be operated conveniently from a singletransmitter.

The calling receiver inthe audio modulated calling system shownin Fig. 3operates as follows: Assume that the tuned circuit 32, 34 is tuned tothecalling carrier frequency and the switch l31 is positioned to closecontacts 38 and 39 so that the message translator 42 is disconne'ctedfrom the receiver 35. An initial pulse of audio modulated callingcarrier frequency energy isreceived by the antenna 30, and passedthrough the transformer 33 and the tuned circuit 32, 34 tothe receiver35 where it is detected. The audio detector output of the receiver 35,the amplitude of which varies in accordance with the modulating audiofrequency of the received calling carrier pulse then passes throughtheamplifier 83', the contacts 38 and 39 of the switch 31, and into thetuned circuit 91 which comprises the condenserA |09 and the inductance99 in parallel. The tuned `circuit 91 is an audio frequency selectivedevice which corresponds in its resonance frequency to one of the`modulating vfrequencies of the audio generators 81A, 81B or 81C. If themodulating frequencyof the received calling carrier signal issuch thatthe tuned circuit 91 is responsive-thereto, the output of the rectier918 `energizes the electromagnet 43, 4,which repre-A and received atthat instant when the selector arm 58 is in engagement Vwith contact 82in jack 8l again energizes the relay 43. This 'causes the signal lamplt'o light as described with reference to Fig. l.

Bymeansofthe system'de'scribed with reference to Fig. 3, thetransmitting operator can call simultaneously a number ofdifferentsetsof subscribers. corresponding to the number of audiomodulated-frequencies@sent outfby the transmit-g ter, inasmuch as eachsubscribingiselector unit contains a tuned circuit responsive to one ofthe several audio modulating frequencies of the transmitter.

Although the invention of the applicant has able contactor, a messagetranslator, a constant-L ly operating motor, an announcing device, meansresponsive to a first pulsed signal received by said radio receiver forcausing the selector to mechanically connect the movable contactor tothe motor, meansresponsive tb a second pulsed signal received by saidradio receiver at a predetermined interval after the preceding signal toenable the motor-driven movable contactor of the selector to actuate theannouncing device and means whereby the selector or the message transf.

lator may be alternatively connected to said output terminals.

2. Radio call receiving apparatus lfor a mobile unit comprising a radioreceiver, a loud-speaker,

a clock, and a signal annunciator device the env,

ergization of which is controlled by the clock, and means foralternatively'connecting the radio receiver to the loud-speaker or tothe annunciator device whereby either radio broadcast program messagesor an annunciator signal individual to.'u

the particular mobile unit may be had from the same radio receiveraccording to which apparatus is connected thereto.

3. An annunciator system for a mobile station comprising a radioreceiver having output termi-i nals, said radio receiver tunable to arange of frequencies including a calling carrier frequency, aloud-speaker, selective call receiving means, an annunciator apparatus,a motor, and means for connecting the radio receiver output terminals tothe loud-speaker or to the selective receiving means alternatively, saidselective receiving means responsive to one impulse of calling frequencycarrier Waves received by said receiver to connect itself to the motorand to a second properly timed impulse of waves of the same carrierfrequency received by said receiver to actuate said annunciator deviceto announce a call.

4. An automobile radio announcersystem for announcing to an occupant ofan automobile that i120 selector mechanism provided with a clutch, meansfor disconnecting said message translator from said receiver' andconnecting said selector mechanism in its stead, means for engaging saidselector mechanism-with the driving mechanism of said motor, vmeans forretaining said selector mechanism in said engagement for a designated 1time interval, a signal device connected to said selector mechanism, andmeans responsive to a calling signal received by said receiver at apredetermined time in said time interval to actuate ,y said signaldevice.

his attention is desired comprising a radio broadcast receiver havingoutput terminals and a loudspeaker electrically connected thereto, aselector having a movable contactor, a clock having a rotating shaft, anannunciator, means for disconnecting the loud-speaker circuit from theoutput terminals of the receiver and connecting the selector in itsstead, means responsive to a calling signal received by the receiveryfor connectingthe selector contactor to the shaft and responsive to asecond calling signal received at a predetermined interval after thefirst for causing the selector contactor to energize the annunciator.

5. In a radio calling system, a call receiving device comprising incombination a radio receiver, a message translator connected thereto,means for tuning said receiver to desiredincoming carrier frequencies;including the calling carrier frequency, a continuously operating motor,al driving mechanism connectedthereto, a

6. In a radio calling system, a calling means including a transmitter,said transmitter comprising in combination a source of carrier frequencyoscillations, a continuously operating motor, a driving Vmechanismconnected thereto, a selector mechanism provided with a clutch, means toactuate said selector clutch to cause said selector mechanism to beconnected to said driving mechanism, means for retaining said selectormechanism connected with said driving mechanism for a designated timeinterval, pulsing means controlled by said selector mechanism to enablecarrier frequency pulses to be transmitted at desired instants in saidtime interval; a plurality of call receiving means each of whichcomprises in combination a radio receiver, means for tuning saidreceiver to desired incoming carrier frequencies including the callingcarrier frequency, a message translator connectedfto said receiver, acontinuously operating motor, a driving mechanism connected thereto, aselector mechanism provided with a clutch, means for disconnecting saidmessage translator from said receiver and connecting said selectormechanism in its stead, means operative upon reception of an initialcalling frequency pulse to cause said selector mechanism to engage thedriving mechanism of said motor, means for retaining said selectormechanism in saidengagement for the desired time interval, a signaldevice connected to said selector mechanism, means to cause said signaldevice to respond to a calling signal received at a predetermined timein said time interval.

'7. In a radio callin'gsystem, a call receiving device comprising incombination a radio receiver, a message translator'connected thereto,means for tuning said receiver to desired incoming carrier frequenciesincluding a calling carrier frequency, a continuously operating motor, adriving mechanism connected to said motor, a selector mechanismcomprising a selector dial, a'removable contact positioned at apredetermined point thereon, a selector arm rotatable'to engage saidmeans responsive to an initial pulse of calling -frequency vreceived bysaid receiver to actuate said selector clutch to cause said selectormechanism to engage the driving mechanism of said motor, means forretaining' said selector mechanism in said engagement for the desiredtime interval, a signal device connected to said contact on saidselector dial,I and means responsive to -a calling signal received bysaid receiver at a predetermined time in said selector cycle to actuatesaid signal device.

8. In a radio calling system, a calling means including a transmitter,said transmitter comprising; in combination 'a source of carrierfrequency oscillations, a selector mechanism com- 11 prising a selectordial, removable contact plugs positioned thereon, a selector armrotatable to engage said contacts in succession, clutching meansconnected to said selector mechanism,fa

continuously operating motor, a driving mechanism connected thereto,means to actuate said selector clutch for connecting said selectormechansm to said driving mechanism, means for retaining said selector.connected to said driving mechanism for a desired ytime interval, meansconnected to said contact plugs to enable pulses of carrier frequency tobe transmitted at desired instants in said selector cycle; Va pluralityof call receiving means each comprising in combination a radio receiver,means for tuning said receiver to a desired calling carrier frequency, acontinuously operating motor," a driving mechanism connected' thereto, aselector mechanism comprising a selector dial, a removable contact plugpositioned at a predetermined point thereon, a selector arm rotatable toengage said contact at a predetermined time in the cycle of rotation ofsaid selector, a clutch connected to said selector mechanism, means toactuate said selector clutch to engage the driving mechanism of saidmotor, means for retaining said clutch in said engagenient for thedesired time interval, a signal device connected to said contact plug onthe selector dial, and means responsive to` a calling signal received bysaid receiver at a predetermined time in said selector cycle to actuatesaid signal device.

9. In a calling system, a call receiving means comprising 'incombination a radio receiver, a vvmessage translator electricallyconnected'thereto,

means for tuning said receiver to desired incom-f ing carrierfrequencies including the calling carrier frequency, a continuouslyoperating motor,

Va driving mechanism connected thereto, a selector mechanism providedwith a clutch, means for disconnecting said message translator vfromsaid receiver and connecting said selector mechanism in its stead,electrically selective means connected in circuit with said selectormechanism' and responsive to current of a predetermined audio frequency,means responsive upon reception by said receiver of an initial callingcarrier fre- Aquency pulse of the audio-modulating frequency Vto whichsaid selector circuit is responsive to cause said selector mechanism toengage said driving mechanism, means lfor retaining said selectormechanism in said engagement for a desired time interval, a signaldevice connected to said selector mechanism, and means responsive toactuate said signal device upon reception by said receiver, at apredetermined'time in said "time interval of a calling signal Vmodulatedaccording to the audio frequency `to Which said selector circuit isresponsive.

10. In a calling system, a calling means including a transmitter, saidtransmitter comprising in mechanism, means for retaining each saidselector mechanism in said engagement for a desired time interval, meanscontrolled by each said selector mechanism to cause pulses ofaudio-modulated carrier frequency to be transmitted at deaired instantsin said time interval; a plurality '12 of call receiving means eachcomprising in combinationa radio receiver, a message translatorconnectedto said receiver, means for tuning said receiver to desiredincoming carrier frequencies including the callin-g carrierfrequency,a'continuously operating motor, a driving mechanism connected thereto, aselector mechanism provided with a clutch, means for disconnecting saidmessage translator from said receiver and connecting said selectormechanism in its stead, electrically selective means connected incircuit relationshipA to said selector mechanism and responsive .to oneof the modulating audio frequencies of said calling carrieroscillations, means responsive upon reception by said' receiverfof aninitial calling frequency pulse of the audio-modulating frequency towhichsaid selector circuit is respon- Vsiveto actuate said clutch toengage the driving mechanism of said motor, means for retaining Vsaidclutch in rsaid engagement for the desired vtime interval, a signaldevice connected to said selector mechanism, means'responsive to actuatesaid signal device upon reception by said receiver V at a predeterminedtime in said time interval of a calling signal vmodulated according tothe audio frequency to which said selector circuit is responsive.

11. In a radio calling system comprising in combination a transmitteradapted to send pulsed carrier frequency signals which may be modulatedalternatively according to respectively different audio frequencies, aplurality of call receiving units, means for tuning each of saidreceiving units to desired incoming carrier frequencies including thecalling carrier frequency of said transmitter, pulse responsive meansconnected to each of said receiving units, a signal device connected toeach said pulse responsive means, said pulse responsive means adapted toactuate said signal `device only in response to calling pulses of apredetermined time relationship, electrically selective means connectedto said pulse responsive means whereby said pulse responsive meansresponds to pulses of only one of the modulating audio frequencies ofsaid calling carrier frequency signals, and switching means to enablethe call receiving equipment including said receiving units and saidpulse responsive means to be at least partially utilized for con-`ventional broadcast reception when said receiv- 'receiving means byconnection thereof to said motor, and signal controlled means responsiveto a second pulsed signal from said receiver following `the first signalbyr a predetermined interval for actuating said announcing device.

' RALPH K. POTTER.

REFERENCES 'CITED The following references are of record in the ViileVof this patent:

UNITED STATES PATENTS Number Name Date 1,464,565 Espenschied v Aug. 14,1923 2,229,097 Koenig 1- .V Y Jan. 21, 19451

